Study Of The Influence Of Ce-doping On The Oxygen Releasing Properties Of Copper Based Oxygen Carrier And CO Chemical Looping Combustion

Not only can it achieve CO₂ separation, but also reduce NOx emissions, an effective method to enrich CO₂, Chemical Looping Comustion?CLC?, is of great importance today when environment attracts increasing attention and energy is increasingly relied on. CLC is first step of Carbon Capture, Utilization and Storage?CCUS?, which can use coal cleanly and efficiently. Oxygen carrier with high performance is reseach foucs of CLC. Doping other metal elements can improve the performance of oxygen carrier. This method to improve oxygen releasing properties of oxygen carrier and CO participation in CLC with the presence of sulfur gases is relatively scarcely studied. Therefore, the oxygen releasing performance of Cerium doped Cu-based carrier and effect of sulfur content gas on CO CLC were studied by Density Functional Theory?DFT? method combining with thermogravimetric analysis.The effect of Cerium on Cu-based oxygen carrier and the mechanism of the effect are not clear. At first, the effect of Ce-doping on oxygen releasing properties of Cu-based oxygen carrier was studied by programmed temperature experiment in thermogravimetric. The results of experiment show that Ce-doping reduced peak temperature at reaction, raised reaction velocity at lower temperature, and promoted oxygen release of Cu-based oxygen carrier. Then the effect mechanism was studied by DFT method. The results of DFT calculation show that Ce-doping reduced energy barrier and reaction heat of O₂ formation on CuO surface, improved reaction heat of O₂ desorption from CuO surface, promoted the migration of inner oxygen atoms to the surface layer. Generally, Ce-doping reduced energy barrier of oxygen release reaction, and then promoted oxygen release of CuO. This phenomenon is manifested by reaction peak temperature dropping and reaction velocity increasing at lower temperature in the thermogravimetric experiment. The results of experiments and theoretical calculations are in good agreement.The effect of H₂ S in syngas on CO in CLC has not been studied sufficiently. After the effect of cerium element on oxygen release property of Cu based oxygen carrier was defined, the effect of Ce-doping on CO in CLC with H₂ S existing was studied by DFT method. When CO and H₂ S adsorbed on CuO?1 1 1? perfect surface synchronously, H₂ S was dissociatively adsorpted. CO and H₂ S promoted each other's adsorption. The number of adsorption sites increased because of oxygen vacancy. Meanwhile the absolute value of CO adsorption energy is larger than that of H₂ S, CO would be preferentially absorbed. The adsorption of H₂ S on this was not stable. So, oxygen vacancy is conducive to the adsorption of CO, not to that of H₂ S. Although Ce-doping has no obvious infuence on the adsorption of CO and H₂ S on CuO?1 1 1? perfect surface separately, the adsorption of CO and H₂ S is in competitive relationship. And Ce-doping promoted oxygen vancacy formation, reduced H₂S's adverse effect on CO adsorption, improved reaction property of CO in CLC.SO₂ is the main transformation product of sulfur content in coal combustion process, and its effect on CLC is rarely studied. The effect of Ce-doping on CO in CLC with SO₂ existing was also studied by DFT method. When CO and SO₂ both adsorbed on CuO?1 1 1? perfect surface, SO₂ would occupy more adsorption sites and be preferentially absorbed because of its strong adsorption ability. So, SO₂ hindered the adsorption of CO on CuO?1 1 1? perfect surface. The adsorption abilities of CO and SO₂ are stronger with oxygen vacancy, and the adsorption of SO₂ is more stable. The asolute value of CO adsorption energy on CuO?1 1 1? oxygen defect surface with SO₂ adsorption is larger that that on CuO?1 1 1? perfect surface. Therefore, oxygen vacancy reduced obstacles of SO₂ to CO adsorption. Three coordination Ce-doping reduced obstacles of SO₂ to CO adsorption. Four coordination Ce-doping is not conducive to the adsorption of SO₂, and has no ettects on CO adsorption on Cu atom. In addtion, Ce-doping promoted oxygen vancacy formation. Therefore, Ce-doping can reduce the adverse effect of SO₂ on CO adsorption, improve reaction property of CO in CLC.